Teufelsberg was just a short distance away from RAF Gatow as the crow flies, but the wide Havel River flowing between the two meant that road traffic had to make a lengthy diversion via the Heerstrasse, a five kilometre, multi-lane highway running from the East German border at Staaken right into the centre of West Berlin. The Heerstrasse, which literally translates as Military Road, was always congested during daylight hours. I had to use it on my way to and from work, and every time I needed to visit the centre of West Berlin on other duties - or for pleasure.

Above: The large building in the foreground was Edinburgh House, a British forces guest hotel for officers and their families, located on one corner of Theodor-Heuss-Platz (named after Theodor Heuss (1884–1963), the first President of Germany after World War II

There were road junctions every few hundred metres along the Heerstrasse, all controlled by traffic lights. I was fascinated, and irritated, by the traffic light control system - very advanced then even by today's standards. Flashing digital light signals every 200 metres or so between junctions indicated the speed to drive at (always between 20 and 50 kph) if you wished to connect with a green signal at the next junction. The system assumed that all drivers obeyed the maximum speed limit of 50 kph, very strictly enforced for all British military vehicles but largely ignored by all others. Berliners were adept at working out how fast they needed to drive, anywhere between 60 and 90 kph, to reach an earlier green signal at the next junction. I suppose they could save several minutes on their daily commute when they got it right, but every now and again one of the drivers got it wrong, slammed on the brakes and caused vehicles behind to brake even more sharply hoping to avoid a nose-tail collision.

Incidentally, during my years in Germany there was a rule that was strictly enforced throughout the country as well as in West Berlin: any driver who collided with the vehicle in front was automatically deemed to be responsible for the collision, irrespective of what the driver in front had just done.

I started work at No 26 Signals Unit on New Year's Day 1978. Most of my first week was taken up with a series of operational briefings and visits to other intelligence organisations within West Berlin. On my first day I attended the standard 'Berlin Briefing' at RAF Gatow that all new arrivals had to go through and then my predecessor took me to Teufelsberg. Before I was allowed to enter the secure area, I had to go through the security re-indoctrination process and only then was I issued with the pass which allowed me unhindered access to the secure areas. On the second day more briefings and then, in the evening, I went to the Philharmonic Hall to hear Elizabeth Schwarzkopf's final Berlin recital before her retirement. I can't now remember how I managed to get a ticket for that highly auspicious event that had, apparently, been over-subscribed for many weeks.

Above: Another image I took just inside the American Sector showing how close you could get to the border - with a fence (presumably electrified) and an East German observation tower barely a stone's throw away. Every time I took an image openly like this, I could be certain that I was being photographed. It was all part of what Rudyard Kipling used to call 'The Great Game'.

On my third day the Director of the US National Security Agency (NSA) visited 26SU; he didn't come specially to see me, of course, but I sat in on his briefing and followed him around. I can't now remember his name, but I believe he was new in the job. On the fourth day my predecessor took me to visit BRIXMIS (the British Commanders-in-Chief Mission to the Soviet Forces in Germany) where I was given a detailed presentation on their role. I learned that BRIXMIS personnel spent most of their time travelling around East Germany. The Soviets, Americans and French each had their own versions of BRIXMIS. The idea, so I was briefed, was that each of the four nations could keep track of what the others were doing and make sure they were not violating any military agreements.

On my fifth day I was ordered, at very short notice, to take the daily RAF flight to the Headquarters of RAF Germany, near Mönchengladbach, to meet the Command Intelligence Officer (CIO), a group captain by rank. He welcomed me and then gave me a warning. Someone had informed him that I had been to BRIXMIS the previous day. It was, he told me, strictly forbidden for personnel of BRIXMIS and 26SU to visit each other's establishments in Berlin, or to exchange intelligence data with them by any means. What the group captain appeared not to know, and I was not about to tell him, was that after visiting BRIXMIS my predecessor had also taken me to the US and French equivalent organisations in West Berlin.

The CIO accepted that I had been to BRIXMIS in all innocence; he said he would deal with my predecessor for having arranged it. The CIO told me that the reason for not allowing liaison between different field intelligence agencies was to prevent what was known in the trade as 'action on'. The assumption was that if two or more field agencies shared, or even discussed, any particular new intelligence and they then unilaterally acted upon it, it might reveal to the Soviets how the intelligence had been obtained. Revealing the source of your intelligence to your enemies was one of the greatest sins in the trade.

The CIO went on to explain that GCHQ always did the analysis of intelligence product in-house at Cheltenham because it was only GCHQ that had access to intelligence from all sources. GCHQ released intelligence to those who were known as 'the customers', defined as those who would actually make use of the intelligence to fight the Cold War. In the case of the RAF, he told me, Strike Command was the major customer.

When I got back to 26SU that evening, relations between me and my predecessor were visibly strained: he didn't ask me what I had learned from the CIO - there had obviously been words exchanged between them but I have no idea what the outcome was.